1. Field of the Invention
The present invention relates to a liquid crystal display device and more particularly to a liquid crystal display device having a writing region of identification information for managing a panel history.
2. Background Art
Conventional liquid crystal display devices include a first substrate formed with pixel electrodes and the like, a second substrate arranged to face the first substrate, and a liquid crystal layer interposed between the first substrate and the second substrate. At the first substrate, in each of regions surrounded by, for example, a plurality of gate lines extending in the x-direction and arranged in parallel in the y-direction and a plurality of drain lines extending in the y-direction and arranged in parallel in the x-direction, a pixel is configured with at least a thin film transistor which is turned on with a scanning signal from the gate line and a pixel electrode supplied with a video signal from the drain line via the turned-on thin film transistor. With this configuration, each of the pixels can be controlled independently, whereby an image is displayed with the pixels.
On the other hand, a black matrix and color filters of R (red), G (green), and B (blue) corresponding to each of the pixels are formed at the second substrate, whereby color display is performed depending on the amount of transmitted light transmitted through the color filters.
In the thus configured liquid crystal display devices, when a trouble has occurred in the liquid crystal display device incorporated into a final product such as a mobile phone, it is required to determine in a short time whether the trouble has been caused by conditions in manufacturing, etc. or has occurred accidentally. Therefore, history information on individual liquid crystal display devices is important.
However, in order to manage the history information on individual liquid crystal display devices, identification information such as a number unique to each of the individual liquid crystal display devices is assigned, and the histories of the liquid crystal display devices have to be managed individually based on the identification information.
A method for managing identification information on individual liquid crystal display devices is disclosed in, for example, Japanese Patent No. 2734183. In the method disclosed in Japanese Patent No. 2734183, a character pad for laser marking is formed by using an opaque film above a glass substrate. Further, a technique for protecting the character pad by using a transparent insulating film formed in a display region in common as an insulating film for protecting the character pad is disclosed.